From the Tanya, Shaar Hayichud Vehaemunah, middle of Chapter 4

For it is not within the power of the intellect of any creature to comprehend through the faculty of Chochmah or understand through the faculty of Binah this attribute and its ability to create a being out of nothing and vivify it.
For creation ex nihilo is a matter which transcends the intellect of all creatures, inasmuch as it stems from the Divine attribute of Gedulah (Chessed).
Now the Holy One blessed be He, and His attributes are a perfect unity, as the holy Zohar states, “He and His causations i.e., His attributes are One,”